1. Field of the Invention
The present invention relates to a control device that controls a drive signal to be supplied from a drive device to a load apparatus in a PWM manner.
2. Description of the Related Art
Conventionally, controlling the drive of an electric load apparatus (simply, load apparatus) has been performed in many ways. Of those, one way is to allow a control device to PWM-control a drive signal to be supplied to a load apparatus with the help of switching elements. The PWM-controlled drive signal provided from the control signal is able to control the drive of the load apparatus. In such a control device, a path connecting the load apparatus and the switching elements is electrically monitored as to whether or not a monitored signal shows changes in response to the PWM signal. If a situation where such changes have disappeared (i.e., no history) is found, it can be estimated that the path has short-circuited. As can be seen from Japanese Patent Unexamined Publication No. 09-196991, this is a typical detecting configuration for the path.
Specifically, in this kind of control device, when the load apparatus has been short-circuited to an H-level (high potential provided by a power supply, which is also referred to as a battery voltage (or battery terminal voltage) represented by “+B”), the monitored signal is forcibly fixed at the H-level irrelevantly to how the PWM signal changes. Unlike this situation, once the load apparatus has been short-circuited to an L-level (the ground level), the monitored signal is forcibly fixed at the L-level irrelevantly to changes in the PWM signal. In other words, since the short circuit suppresses the monitored signal form changing in response to those in the PWM signal, it is possible to estimate that a short circuit has occurred.
Thus depending on the monitored signal is fixed at which level, what kind of short circuit, that is, H-level short circuit or L-level short circuit, can be determined.
By the way, while the conventional system adopts a configuration in which switching elements are arranged between a control device and a load apparatus, recent systems adopt a different circuitry. Specifically, instead of the switching elements, a drive device is arranged in which one or more versatile IC chips having a plurality of switching elements and circuits for other functions are integrated. This arrangement aims at saving not only handling work for arranging plural switching elements but also costs for the arrangement in cases where the operations of a plurality of load apparatuses are controlled respectively and/or additionally having functions other than the PWM control with the switching elements.
Such a drive device may normally have a function of detecting the occurrence of short circuit from signals to be fed to or outputted from the switching elements and informing it toward the outside of the drive device. Even if so, this drive device still suffers from the drawback that it is impossible to determine and inform that the short circuit occurred at which level, or at the H-level or the L-level. Hence only information indicating the occurrence of the short circuit is still insufficient, because it does not provide any information showing that the short circuit occurs at which potential side.
This problem could be resolved if the drive device is formed to determine whether a short circuit is occurring at the H-level side or the L-level side and to notify an outside apparatus of the determined results. However, additionally providing such functions to a drive device results in that the drive device cannot be handled as a versatile device any longer, whereby costs for manufacturing the drive devices will be raised.
Therefore, it is desirable that a versatile device can be used as much as possible as the drive device. In addition, it is also desirable if such a versatile type of drive device can be used, as it is (without redesigning), to detect information about a short circuit and the information from the drive device can be processed by another device to determine that the short circuit is occurring at which potential level.